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990. Satisfiability of Equality Equations 👍

  • Time: $O(n\log n)$
  • Space: $O(n)$
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class UnionFind {
 public:
  UnionFind(int n) : id(n) {
    iota(id.begin(), id.end(), 0);
  }

  void union_(int u, int v) {
    id[find(u)] = find(v);
  }

  int find(int u) {
    return id[u] == u ? u : id[u] = find(id[u]);
  }

 private:
  vector<int> id;
};

class Solution {
 public:
  bool equationsPossible(vector<string>& equations) {
    UnionFind uf(26);

    for (const string& e : equations)
      if (e[1] == '=') {
        const int x = e[0] - 'a';
        const int y = e[3] - 'a';
        uf.union_(x, y);
      }

    for (const string& e : equations)
      if (e[1] == '!') {
        const int x = e[0] - 'a';
        const int y = e[3] - 'a';
        if (uf.find(x) == uf.find(y))
          return false;
      }

    return true;
  }
};

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class UnionFind {
  public UnionFind(int n) {
    id = new int[n];
    rank = new int[n];
    for (int i = 0; i < n; ++i)
      id[i] = i;
  }

  public void unionByRank(int u, int v) {
    final int i = find(u);
    final int j = find(v);
    if (i == j)
      return;
    if (rank[i] < rank[j]) {
      id[i] = j;
    } else if (rank[i] > rank[j]) {
      id[j] = i;
    } else {
      id[i] = j;
      ++rank[j];
    }
  }

  public int find(int u) {
    return id[u] == u ? u : (id[u] = find(id[u]));
  }

  private int[] id;
  private int[] rank;
}

class Solution {
  public boolean equationsPossible(String[] equations) {
    UnionFind uf = new UnionFind(26);

    for (final String e : equations)
      if (e.charAt(1) == '=') {
        final int x = e.charAt(0) - 'a';
        final int y = e.charAt(3) - 'a';
        uf.unionByRank(x, y);
      }

    for (final String e : equations)
      if (e.charAt(1) == '!') {
        final int x = e.charAt(0) - 'a';
        final int y = e.charAt(3) - 'a';
        if (uf.find(x) == uf.find(y))
          return false;
      }

    return true;
  }
}

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class UnionFind:
  def __init__(self, n: int):
    self.id = list(range(n))

  def union(self, u: int, v: int) -> None:
    self.id[self.find(u)] = self.find(v)

  def find(self, u: int) -> int:
    if self.id[u] != u:
      self.id[u] = self.find(self.id[u])
    return self.id[u]


class Solution:
  def equationsPossible(self, equations: list[str]) -> bool:
    uf = UnionFind(26)

    for x, op, _, y in equations:
      if op == '=':
        uf.union(string.ascii_lowercase.index(x),
                 string.ascii_lowercase.index(y))

    return all(
        uf.find(string.ascii_lowercase.index(x)) !=
        uf.find(string.ascii_lowercase.index(y))
        for x, op, _, y in equations
        if op == '!')